In the industrial automation or the electric carrier field nowadays, there is an increasing demand for inverter capable of handling high voltage and high loading, which brings many challenges in designing a power module. One of these challenges is designing terminals of the power module, which are connected to an outer circuit. The outline and arrangement of the terminals will affect a stray inductance value of the power module. If the design is improper, the stray inductance value will be overly high, and products with low breakdown voltage will be damaged easily. Besides, the terminals are usually soldered to the substrate, so there is a high possibility of solder cracking, and the cracks are tending to enlarge, leading to malfunction of the product. Moreover, during the process of fixing the outside circuit to the terminals by screws or the likes, an external force is exerted to fasten the screw, however, this force is also imparted to the solder where the terminal and the substrate are bonded, thus causing the crack to be generated or enlarged.
Please refer to FIG. 1, a perspective view showing a conventional power module structure. The power module 100A includes a substrate 1A and a plurality of switch units 2A. A bottom of the switch units 2A is in physical contact with and is electrically connected to a first terminal 31A, and a surface of the switch units 2A is electrically connected to a second terminal 32A with a wire. As shown in FIG. 1, it is required to arrange the switch units 2A parallel to each other in order to reduce parasitic inductance, and each of conductive areas 11A, 12A of the substrate 1A forms a U-shaped circuit to achieve the parallel arrangement of the switch units 2A. On the premise that the design can withstand voltage as required, a distance between the conductive areas 11A, 12A should be as small as possible. Moreover, it is also necessary to arrange the first terminal 31A and the second terminal 32A parallel to each other, and to make a distance therebetween as small as possible, on the premise that the design can withstand voltage as required, so as to reduce inductance. However, the power module 100A still has a large crossover area, so it is still difficult to reduce stray inductance of the whole circuit sufficiently.
Please refer to FIGS. 2A and 2B, a perspective view showing another conventional power module structure and a schematic view showing a metal board of another conventional power module structure. The power module 100B includes a plurality of switch units (not illustrated) and a plurality of terminals 31B, 32B, 33B. The switch units are soldered to conductive areas 11B, 12B of a substrate 1B. The terminals 31B, 32B, 33B are also soldered to the substrate 1B which connected the signal between an outside circuit and power units inside. A metal plate 4 is provided at an outer side of the three terminals 31B, 32B, and 33B to reduce inductance effectively.
The metal plate 4 serves to generate a reversed current when a current flows through the third terminal 33B from the first terminal 31B or flows through the second terminal 32B from the third terminal 33B. The reversed current generates a magnetic field that against the current of the terminals 31B, 32B, and 33B to reduce inductance. According to FIGS. 2A and 2B, the power module 100B mainly improves the terminals 31B, 32B, and 33B, however, it also fails to reduce the crossover area of the power module 100B.
Therefore, the inventor aims to solve the aforesaid problems by inventing a low-stray-inductance power module having a packaging structure, wherein a plurality of terminals and a plurality of switch units are arranged parallel to each other to reduce inductance of the power module and to achieve uniform current distribution. In addition, by means of the structure design, the terminals are bonded strongly to thereby improve reliability and to prolong a lifespan of the power module.